The Lake: Internal Waves

Sam Kelly is the first guest of Season 2 of home. Follow the links below to learn more about his work. I learned a lot in this interview and I hope you enjoy it also!

https://schmidtocean.org/person/sam-kelly/

https://www.d.umn.edu/~smkelly/

(This episode will be released just as the first finishers of the Gary Bjorklund Grandma’s half marathon cross the finish line in Canal Park, having raced 13.1 miles along Lake Superior for the 30th annual race. 24,000 people were estimated to compete in the various Grandmas races this year)

Check out the internal waves in the episode photo, taken by B Greenfield on 6/19/26 from Palisade Head.

Transcript

SPEAKER_00 0:00

way back came into my office and he just like ran his microphone for 10 seconds um to get like the background oh really ambient noise or something and then he's like how you can I'm gonna use it to like do the blend like the transition blend so that it doesn't it doesn't sound like they just like flip taped you know when you go from like the person in the studio to like the story and the you know that they're they were recording in my office.

SPEAKER_01 0:27

I ran into trouble with that because I would sometimes like record an ad at the start and then the sound would be so different from the podcast. Yeah so I was like I don't know what to do about that but yeah so do we do we need to be talking do we have to like you just talk to me.

SPEAKER_00 0:44

Okay it's good it's perfect okay um hi Sam hi Bruna how's it going yeah pretty good yeah um thank you for doing this uh kind of impromptu yeah podcast with me this is um home and season two is the lake and we're talking about Lake Superior today which I hear you might know something about we spent a little time on it yeah it's uh it's the best lake so really I think so why is it the best lake it's uh it's big and uh interesting and it's also like really pristine you know really clean water and you know not a lot of development around it so it's just a beautiful place.

SPEAKER_01 1:31

Awesome um what's your first memory of like water and being connected with water outdoors?

SPEAKER_00 1:38

Uh well growing up in the Twin Cities like just going swimming at like our local small lakes which are always you know in the summer they're like warm and you know catching sunnies and swimming out to you know swimming docks and you know floating rafts and jumping off of those um yeah nice um I was reading that you study internal waves yeah which are different than top waves right right what do you call waves on top of the water surface waves surface waves okay yeah so like how are they different right so uh in a in a big lake you usually you often get like warm water at the surface and colder water underneath uh and you can kind of think of that like oil and water and so you can have a wave at the surface but you can also have a wave between the two fluids and so I study these internal waves in Lake Superior they exist like from around July through like the end of maybe October and um they're usually found anywhere from you know five meters down to 30 or 40 meters down.

SPEAKER_01 2:47

So do they look like waves like I think of them?

SPEAKER_00 2:51

Like are they that like they they are really big and really slow. So a surface wave might have a a height of you know a few feet and then these internal waves can have a height that's maybe 20 or 30 feet you know um and but instead of oscillating you know every couple of seconds or several times a second they oscillate uh you know over the course of hours so there's these like big slow um waves that um move water around and little organisms ride on them and get moved around too so they're kind of important for things that live under the water is it like all across the lake that there's internal waves yeah right so pretty much once once the summer warms up that that surface layer you know the the the heat from the sun really never gets down to the to the bottom of the lake so the bottom of the lake stays about four degrees Celsius. How much is that on Fahrenheit? That's like around 40 degrees okay so and and then the surface you know can warm up to 60 70 degrees and uh yeah basically there's a there's an old quote by uh Walter Monk who's a famous oceanographer that no one's ever observed an internal calm that whenever you go and make measurements under the water you always see these these waves going up and down. But you said they're not always there though no uh oh right uh ex uh when there's when there's layers of water when you have the difference in temperature you always have internal waves um and then when the difference in temperature goes away like in the winter or in the late fall um the surface cools to the same temperature as the bottom and then you have sort of a uniform oh yeah it's just like one big glob. Right right one big lab and then and then the whole water moves together and you don't get you don't get the waves in the in uh internal waves.

SPEAKER_01 4:46

So how does that impact like animal or like fish like life in the lake like do the internal waves you said they like move them around a little bit yeah so uh there are places where like the when the waves go up they carry things with them and they might bring them up into an area where there's a little more sunshine and so um yeah you um they can bring nutrients up I guess into the sunshine and then when you have nutrients and sunshine you get algae growth and then when it goes back down then you take it out of the sun and that kind of damps the growth so um yeah and they can also sometimes they get really big and they can actually like entrain stuff and kind of carry it with them.

SPEAKER_00 5:26

So you like if you have a way of propagating say you know westward across the lake it could be taking some fish eggs with it or uh some pollution some microplastics or something right so they can actually transport things around the lake.

SPEAKER_01 5:42

Not people though or like not like big fish. Does that move is it like strong enough to move fish underwater?

SPEAKER_00 5:48

They're not so strong in the in Lake Superior that they do that. In the ocean there are internal waves that um you know can can like yeah they could suck they could suck a person down like if you were swimming right you and you got pulled into one of them and and sucked down into the trough uh you know they can produce vertical vertical currents of like two miles per hour so like big big that's like pretty strong that's faster I think than I can probably swim. Uh-huh yeah uh so yeah it can be powerful that's cool yeah um what do you think is like something that you find really interesting about Lake Superior that most people don't know hmm uh well I would say like it's it's a great place to to live by I I I work with all these oceanographers that's my my background is in oceanography and all these people study the ocean and most of them live in coastal cities but they never really see the ocean because you know you could live in Pasadena and not get to the beach more than a couple times a year. And we live you can live on Lake Superior in Duluth and you see the lake every single day sometimes sometimes several times a day and uh I don't know it's just really accessible. It's just a like a you know you can it's not so busy that you can't like park and go swimming you know whenever you want and yeah so I I think I I imagine all my friends from the the coast and they you know they fly over the Midwest and they have never seen the Great Lakes and they they don't they don't know what they're missing.

SPEAKER_01 7:29

Yeah yeah it is pretty amazing it is more accessible than like um beaches on the coast or other things like that for sure. Yeah.

SPEAKER_00 7:37

Yeah and it's I I love uh I just love how cold and refreshing it is to swim and I mean I think a lot of people think it's sometimes too cold but uh I it to me it just feels refreshing. I love it.

SPEAKER_01 7:49

Yeah yeah so yeah I was gonna ask you like how do you like to like interact with the lake like swimming what are other ways you like to like engage with the lake or connect with it?

SPEAKER_00 8:00

Yeah I mean mostly just looking at it like every day you look at it and and uh it's different right the light hits it differently the depending on the weather and the season sometimes it's you know steaming you know like like a giant hot tub and other times it's you know sparkling like it looks like the most beautiful place in the Mediterranean and yeah so I just love to see it every day and see what it what it's what its mood is. Um but I mean it's also just great for recreating I mean paddleboarding and sailing and all those things are great. I wish I had more time to do those things but I know me too I keep telling myself when I retire I'll be you know for sure sailing every week in the regatta or something but I've been too busy so far.

SPEAKER_01 8:47

But you get out on the lake for your research right yes yeah like how long what are what's the usual stretch for how long you go out on Lake Superior?

SPEAKER_00 8:55

Uh the longest I've been out was 14 days straight. That's a long time to be on a relatively small boat. Why what happened? Well it's uh um they're just like it's a working boat and so it just is loud and you know smells it's burning a lot of diesel so it smells like diesel and the cook is really good so you're eating a lot of good food but you know there's not a lot of places to get exercise so you just it's nice to be able to get out and go for a walk.

SPEAKER_01 9:24

Like do you like hop off the boat and swim when you're out there or is it too cold?

SPEAKER_00 9:29

Or dangerous so the the the blue heron are you know our vessel here is a part of the Yunal's fleet which is a fleet of global research vessels and they have a a blanket rule that no one can swim off of boats because someone got attacked by a shark in like the 1980s or 90s. And so now even though we're in Lake Superior we still are not allowed to go swimming off of it because it's a Yunl's boat and there's no swimming rule. That seems silly it is definitely silly. Yeah if you could swim off of it would you absolutely really yeah like you're not nervous to hop in the water in the middle of the lake no no not at all why aren't you nervous about swimming in like the middle of the lake well what's there to be nervous about I mean uh I mean the only thing I would ever get nervous about is that just if it's really cold and you jump in and it's just shocking right and then you can kind of like lose your breath for a second but uh no I it's uh well I mean that maybe another thing people don't know about the lake is just how fast it can change right so yeah so you can be out there and it's just like like very calm like so calm that it's like hot and sticky and just you know you feel like you're just floating around on this big pond and it's and then and then you know an hour later it the wind can be blowing 25 miles an hour and you have three foot waves and and you're just getting tossed around but uh yeah so I guess uh when it's calm like that it's not it's not very uh intimidating but then when the wind picks up and the waves pick up why does that change so quickly you know I don't know I I think I think part of it is that there's no we don't get these long distance uh swells so so a lot of places like in California for instance even if there's no local wind you can get waves from uh you know Alaska or from you know Antarctica that are that literally cross the ocean and and come to California and um you know so so the water's not that calm and and so then if you get local wind then you get some waves on top of those other waves and maybe it's not so different but in Lake Superior you know it's not big enough that you get like waves coming from thousands of miles away. And so it's like can be super calm and then I guess when the the local wind starts blowing then then the waves just feel like they whip up out of nowhere. Because it was calm before yeah yeah and I would say like people would argue we do get some swell in Lake Superior like if you could get some waves generated over in you know Sault Ste Marie that propagate to you know to the to the western side like they're blown over by wind or what yeah yeah and they take like well I I don't know what the time is maybe a couple days I think to to blow over I mean I know if you're a surfer there's like a very small window for when the waves are good so you gotta like really get to the spot exactly when they hit yeah but yeah so anyways so the my point is like sometimes you're out there and you're like wow this is just like the most peaceful place ever and then you know it can be a couple hours later you're just like oh my god give me off this boat like yeah yeah yeah yep I've experienced that it changes so quickly um so what are you like from a research standpoint like what are you um wondering about right now with internal waves in Lake Superior? Yeah well internal waves for sure um or there are other things in the lake yes what are your other like questions so the other thing that I've been thinking about recently is well people are interested in ice and I think we don't know that much about ice because it's hard to get out there in the middle of winter and make measurements when the ships are all you know in in dock and and we don't have an icebreaker that can bang its way out there. So we don't know a ton about winter conditions. But the thing I'm I'm super interested in are just like the is that are the eddies out there right there are these there are these coastal currents and then they um you know as they flow down along the the boundaries they start to um you know become unstable and they form these little gyres that are maybe anywhere from five to ten kilometers across and then those things just keep spinning and they kind of uh drift offshore and they're not really resolved by any of our forecasting models um because they're too small and we don't have a we don't have a ton of like observations of them because they're kind of small and fast and you just have to be out there looking for them I guess so yeah I'm just kind of interested in like what's you know you can kind of think of it as like large scale turbulence in the lake like these turbulent eddies that are just being generated all over the place and propagating for a few days we're listening to a podcast now about that has a vortex in the water yeah okay that um these kids have to go into to be transported back.

SPEAKER_01 14:31

Like do you think it's like a vortex?

SPEAKER_00 14:32

Yeah yeah yeah these are like yeah sure they're vortexes and and um vortices and uh um I don't I don't think I don't they're not like super persistent like you can have an eddy in the ocean that will stick together for like months as it slowly drifts across the ocean. We don't have anything quite like that but you know they might stick together for a few days.

SPEAKER_01 14:53

Really?

SPEAKER_00 14:54

Yeah and they're like moving yeah yeah and presumably they could trap stuff inside of them and sort of like you know move it offshore or onshore from offshore you know so the lake's really cool. Yeah I mean it's also just like a really fun uh you know academic problem of like these this crazy giant turbulence stuff going on in the lake.

SPEAKER_01 15:15

Like do you want to find a mathematical model or a physics equation for it?

SPEAKER_00 15:19

Yeah I mean that's that's kind of like or just like a description of it even like uh you know turbulence is one of the big unanswered questions in general in uh in science so you know thinking about how that applies to lake superior is kind of cool. You know and I think it's one of those things where you just look into something interesting and eventually it'll have some practical application like you know maybe it's important for pollution or or um ecology or something like that. But that's super cool. Yeah yeah um well we're uh basically at the end of our conversation okay um thanks for doing this with me yeah so my last question is um what do you wish for yourself and the lake in the future what do you yeah yeah I mean what I yeah I just hope it can continue to thrive you know I I always kind of get like a sinking feeling when we have a weird winter you know and it's like wait where weren't we supposed to get more ice and you know it feels like things are changing and I just hope that uh that the lake you know is as beautiful you know in 50 years for our kids as and our grandkids as it is for us today you know so yeah that's a great wish thank you Sam yeah yeah thanks for having me